1. Field of the Invention
The field of the invention is that of components for the processing of polarized microwave signals and, more particularly, duplexers of circularly polarized waves. These components may notably constitute a stage of a transmitter and/or a receiver of circularly polarized waves in microwave applications.
In a known way, in satellite transmission, the waves transmitted are often circularly polarized. The reception of a circularly polarized wave is done by means of two antennas, one of the antennas being polarized vertically and the other being polarized horizontally. Thus, the vertical and horizontal components of a right-hand circularly polarized wave are each received by a distinct antenna and may be combined by power coupling to reconstitute the circularly polarized wave transmitted. The same reasoning may be applied to a left-hand circularly polarized wave. The vertical and horizontal components received should have a differential phase-shift of 90 degrees precisely, to avert a power loss in the system.
An object of the invention is to provide a duplexer providing notably for this function of recombination of the linear components of a circular wave received or, inversely, for the decomposition of a circular wave into its linear components at transmission.
2. Description of the Prior Art
There are known devices for the recombination, at reception, of the circular wave received by two antennas at 90.degree.. These devices are usually formed by a three-port hybrid structure. Such three-port hybrid structures are described, for example, in the journal "R. F. Design", July 1989, pp. 56 to 59. This document describes hybrid structures consisting of pi or Tee type Wilkinson combiners/dividers. Wilkinson combiners/dividers are highpass or lowpass filters that can be used either to obtain the sum of two signals or to divide a single signal into two equal signals, depending on their use.
In a known way, the same type of hybrid structure may also be used at transmission to decompose the wave to be transmitted into two components, a horizontal and a vertical component, applied to a set of two antennas with orthogonal polarizations.
It is quite clear that each of these components cannot work simultaneously in transmission and in reception. In fact, with components of this type, a device that has to both transmit and receive circular waves requires two distinct signal processing units working with two distinct local oscillators, one used for the reception of the signals and the other for their transmission.
However, there is a need for compactness and convertibility of components of this type, especially in onboard applications, where it is advantageous to make one and the same component fulfil several functions when possible.
The present invention is designed notably to meet this need.
More precisely, an object of the present invention is to provide a duplexer structure that can be used, when it is linked to a set of antennas, to transmit circularly polarized signals, right-hand as well as left-hand (with the same structure), from the vertical and horizontal linear polarizations of a microwave signal.
Another aim of the present invention is to provide a structure such as this that also enables the reception of right-hand as well as left-hand circularly polarized waves from the vertical and horizontal linear polarizations of a microwave signal.
Another aim of the present invention is to provide a structure such as this enabling the simultaneous transmission and reception of crossed circularly polarized signals.
Another aim of the present invention is to provide a duplexer such as this having an operating frequency band of about 11.7 to 12.5 GHz.
An additional aim of the present invention is to enable a two-way structure such as this to be made by MMIC (monolithic microwave integrated circuit) technology, for example on gallium arsenide, notably to reduce its bulk and its consumption.